The present invention mainly relates to an optical transmission module for use in an optical transmission system or an optical exchange system, and in particular relates to an optical coupling technology, such as an optical wave-guide, a light-beam spot converter and so on, for obtaining an optical coupling with a high efficiency, for instance, between a light emitting or light receiving element and an optical fiber, a light emitting or light receiving element and an optical circuit in the optical transmission module, and/or between the optical circuit and the optical fiber, as well as for obtaining easy install and manufacture thereof.
With development of an optical information transmission path or network, a plan of applying an information transmission with use of an optical fiber was made, not only for use in a business building for various industries, but also into a condominium and/or a separated house or building. One of the important problems therein, needless to say, but is in lowering of a price for such the optical transmission system, in particular the lowering of the price of the optical transmission module, which is connected to a general subscriber at a terminal. For the purpose of great reduction of the cost of the optical transmission module for the subscriber, in recent years, an attempt was made of putting a semiconductor laser having a converter of a light beam-spot diameter into practical use. This is an attempt to aim the low cost of it by means of a method for mounting an optical device(s) or element(s) on a single or a one flat surface and of removal of lenses, and can be understood or interpreted to let the semiconductor laser to own a lens function by itself, so as to remove the lens therefrom. This converter of the light beam-spot diameter, i.e., as a magnifier for the light beam-spot diameter, does not necessarily have a sufficient performance or power in the lens function, however the light beam after emission is narrowed in an extent thereof, thereby improving the optical coupling directly to the optical fiber, or the like, comparing to that of the laser device of the conventional type. As a result of this, the optical module can be assembled with ease and the mounting thereof also can be simplified, thereby advancing the attempt of the reduction in manufacturing cost by a one step.
However, in the converter for the light beam-spot diameter according to the conventional art, there was applied or practiced a technology of selective crystal growth, for the purpose of shaping an edge of a core portion at an emission side thereof in a taper-like. Providing the converter of the light beam-spot diameter inside or outside of the laser resonator, however, in both cases, it comes to bring about problems, such as giving an influence onto optimal designing of the laser itself, or making an effect due to an error(s) in manufacturing process thereof to a lasing ability sensitive. Because of those reasons, a yielding rate in manufacturing the conventional type laser is deteriorated or lowered, and then it rises up the price of the laser itself, thereby coming to be a main cause or factor of deceleration in progress of the steps for the cost reduction of the optical transmission module.
A limit in the magnification of the spot diameter by means of the shaping in the taper-like with use of the technology of selective crystal growth, at the present situation, is ten (10) degree or more or less, being expressed by a radiation angle of far-field pattern with the Gauss beam approximation. Therefore, even in a case of applying a laser having the magnifier of the light beam-spot diameter, further inventions and/or innovations are necessary in relation to novel technologies on the optical coupling, other than those on the semiconductor laser, for the purpose of increasing the optical coupling efficiency and of further facilitating the fabrication thereof. On a while, explaining by use of a coordinate system which is used in the description of the present invention, the conversion of the light beam-spot is relatively easy only in a direction of y axis, but is rather difficult in a direction of x and also in the both directions x and y thereof. Theoretically, it can be realized by tapering the core in the direction of x axis and it was also actually practiced by using such the method on the semiconductor laser, however it necessitates the selective crystal growth technology as mentioned in the above. Therefore, it is difficult to introduce the method onto an optical wave-guide path of quartz as it is, for example, it cannot be said that it is a general method which can be applied to for realizing it cheaply. Also, as an other conventional art method for magnifying the diameter of the beam-spot in the both directions of the x axis and y axis, there was also known a method, in which the core is continuously enlarged or magnified in the diameter thereof, by heating the edge portion of the optical wave-guide path formed on a substrate made of silicon or glass, so as to thermally diffuse dopant in the core portion thereof. However, it is extremely difficult to conduct such the thermal diffusion only onto the edges of the optical wave-guide paths if they are provided in a plurality number thereof on a one (1) wafer, therefore it cannot be said to be a method being high in productivity, nor to be a means being suitable for the cost reduction.
Further in the semiconductor laser of an alley type, the practical, use of the laser having the converter of the light beam-spot diameter itself is not achieved nor realized yet, and with a parallel optical transmission module with use of such the alley-type semiconductor laser, it is necessary to introduce an micro-lens array, etc., thereby making it further difficult the lowering of price of the parallel optical transmission module.
Also, with a module comprising an optical circuitry which is achieved by an optical wave-guide provided between the semiconductor laser and the optical fiber, it is impossible to optimize both the optical couplings between the semiconductor laser and the optical circuitry and between the optical circuitry and the optical fiber at the same time, not so far as the radiation angle of the far-field pattern of the semiconductor laser is nearly equal to that of the optical fiber, therefore there is a problem that the optical circuitry must be designed under a condition of making sacrifices for the respective optimizations thereof. Alternatively, on the contrary to that, there is also a problem that there must be scarified a subject, such as small-sizing of the optical circuitry, for giving the priority the efficiency of optical coupling.
An object of the present invention, therefore, for dissolving the problems mentioned above, is to provide a cheap and small-sized optical wave-guide and an optical beam-spot converter, which can be provided voluntarily between optical parts relatively.
Also, an other object of the present invention is to provide an optical wave-guide and an optical beam-spot converter, which can be realized by an extremely simple process, thereby obtaining lowering of the price therefor.
A further other object of the present invention is to provide an optical transmission module for realizing the ideal optical couplings between bot-h ends of the optical circuitry composed of the optical wave-guide(s) and the optical element(s) and the optical fiber(s), respectively, thereby achieving an improvement on utilization efficiency of light and on easiness or facility in the fabrication thereof.
Moreover, a further other object of the present invention is to provide an optical transmission module, in which an optical beam-spot converter can be easily manufactured on a substrate, on which the optical circuitry and the optical element(s) are mounted, thereby obtaining the lowering of the price therefor.
According to the present invention, for resolving the above-mentioned problems, there is provided an optical wave-guide having a z axis as an optical axis in a direction of propagation of light, a x axis in a vertical direction on a cross-section being perpendicular-thereto, and a y axis in a horizontal direction, comprising:
a core portion being formed so that a light is transmitted in the direction of the z axis, around at a center of an origin of said x axis and said y axis; and
a crud layer surrounding said core portion and being lower in refractive index than that of said core portion, and being constructed with at least two layers, being different in refractive indexes thereof, which are in contact with each other on a boarder laying on a x coordinate in a positive or a negative region thereof but not the origin, wherein
said core portion is formed discontinuously in the direction of said optical axis.
Also, according to the present invention, there is provided an optical wave-guide having a z axis as an optical axis in a direction of propagation of light, a x axis in a vertical direction on a cross-section being perpendicular thereto, and a y axis in a horizontal direction, comprising:
a core portion being formed so that a light is transmitted in the direction of the z axis, around at a center of an origin of said x axis and said y axis; and
a crud layer surrounding said core portion and being lower in refractive index than that of said core portion, and being constructed with at least two layers, being different in refractive indexes thereof, which are in contact with each other on a boarder laying on a x coordinate in a positive or a negative region thereof but not the origin, wherein
said core portion is formed discontinuously in the direction of said optical axis, with varying a width of the core and a length of the core in the direction of the optical axis, and also a length of a portion of the core which is removed, non-cyclically.
Further, according to the present invention, there is also provided an optical beam-spot converter, including an optical wave-guide having a z axis as an optical axis in a direction of propagation of light, a x axis in a vertical direction on a cross-section being perpendicular thereto, and a y axis in a horizontal direction, comprising:
a core portion being formed so that a light is transmitted in the direction of the z axis, around at a center of an origin of said x axis and said y axis; and
a crud layer surrounding said core portion and being lower in refractive index than that of said core portion, and being constructed with at least two layers, being different in refractive indexes thereof, which are in contact with each other on a boarder laying on a x coordinate in a positive or a negative region thereof but not the origin, wherein
said core portion is formed discontinuously in the direction df said optical axis, whereby varying an optical beam-spot.
Furthermore, according to the present invention, there is also provided an optical beam-spot converter, including an optical wave-guide path having a z axis as an optical axis in a direction of propagation of light, a x axis in a vertical direction on a cross-section being perpendicular thereto, and a y axis in a horizontal direction, comprising:
a core portion being formed so that a light is transmitted in the direction of the z axis, around at a center of an origin of said x axis and said y axis; and
a crud layer surrounding said core portion and being lower in refractive index than that of said core portion, and being constructed with at least two layers, being different in refractive indexes thereof, which are in contact with each other on a boarder laying on a x coordinate in a positive or a negative region thereof but not the origin, wherein
said core portion is formed discontinuously in the direction of said optical axis, with varying a width of the core and a length of the core in the direction of the optical axis, and also a length of a portion of the core which is removed, non-cyclically, whereby varying an optical beam-spot.
Also, according to the present invention, the optical wave-guide or the optical beam-spot converter as defined in the above, wherein a portion of said core portion is enlarged in the direction of the y axis so as to form the core portion in a rib type.
Further, according to the present invention, the optical wave-guide or the optical beam-spot converter as defined in the above, wherein a lower portion of said core portion is enlarged in the direction of the y axis so as to form the core portion in a rib type, and a refractive index of a lower crud layer which positions at a lower portion side of the core portion is smaller than that of an upper crud layer which positions at an upper portion side of the core portion.
Further, according to the present invention, the optical wave-guide or the optical beam-spot converter as defined in the above, wherein on a cross-section of the optical axis, a core member is further provided in vicinity of the core portion, which is made of a material same to the core portion or of a material having a refractive index about similar thereto, and which is formed by extending in the direction of the y axis with a thickness being thinner than that of the core portion.
Further, according to the present invention, the optical wave-guide having a crud portion and a core portion, wherein the pattern of the core portion is made in a specific shape, thereby achieving the function of the optical beam-spot conversion by using only a phenomenon of transmission of light in a case where the refractive index of the crud portion is set to be a specific value. Namely, according to the present invention, there is provided the optical beam-spot converter, wherein the core is made discontinuous for the purpose of small-sizing, and the crud layer is constructed with at least two layers being different in the refractive index to each other for the purpose of beam-spot conversion in the x axis direction, thereby achieving those by combining the relationship in magnitude of the refractive index within the crud layer and the discontinuous core configuration thereof.
Further, according to the present invention, the optical wave-guide or the optical beam-spot converter as defined in the above, wherein on a cross-section of the optical axis, a refractive index of a lower crud layer which positions at a lower portion side of the core portion is smaller than that of an upper crud layer which positions at an upper portion side of the core portion, and a core member is embedded into said lower crud layer in vicinity of the core portion, which is made of a material same to the core portion or of a material having a refractive index about similar thereto, and which is formed by extending in the direction of the y axis with a thickness being thinner than that of the core portion.
Further, according to the present invention, there is provided an optical transmission module comprising: a light emitting element or an light emitting element and an optical fiber, and further comprising the optical wave-guide mentioned in the above, being provided with the light emitting element or between the light emitting element and the optical fiber.
And, further, according to the present invention, there is provided an optical transmission system comprising the optical transmission module mentioned in the above, whereby an information is transmitted by means of said optical transmission module.
As is explained in the above, with the construction mentioned in the above, it is possible to realize a small-sized optical beam-spot converter with low cost of manufacturing, independent upon the light emitting element, such as the semiconductor laser or the light receiving element.
Also, with such the construction mentioned in the above, the small-sized optical beam-spot converter can be achieved, in particular with the optical transmission module containing the optical circuit therein, which can operate independently or even if it is connected to both input and output portions of the optical circuit or either one thereof, or alternatively which can be manufactured with the optical circuit as is a form of a one body or unit, and which can optimize the optical coupling at the input and output portions independently and respectively, thereby realizing the optical transmission module with high performances and a low price.